Slice it thin and grill it over high heat for 2-3 minutes per side (it cooks like a lean steak). For the best results, marinate it first: a simple mix of olive oil, garlic, citrus juice, and salt for 2-4 hours tenderizes it and balances the flavor.
You could also cube it and slow-cook it in a braise for 2-3 hours. Or, grind it and mix it into ground beef for extra nutrition while hiding any organ flavor (although heart doesn't have too strong a taste anyway).
Want to use it as lunch meat? Simply simmer the whole heart in salted water for 2-3 hours until tender, let it cool completely, then slice it thin. It holds up well on a sandwich. Mild, meaty, and satisfying.
Beef heart is an actual muscle, the hardest-working one in the animal. It has the texture and flavor of very lean beef more than traditional organ meat. Rich in CoQ10, B vitamins, and iron.
Keep frozen until ready to use for up to 12 months. Thaw in the refrigerator overnight, or quick thaw in a bowl of cold water if you're in a hurry (just keep it in the sealed package). Keep thawed beef heart in the fridge for 1-2 days, or refreeze immediately if not using.